It doesn't sound like it, but wait a bit and take another test just in case. Good luck to you.
I've been working out like crazy myself & I too have noticed that my appetite has picked up - my husband explained the reason (can't remember it right now - LOL). With a negative FRER, I too assume you're not pregnant
Exercising will increase your appetite for sure. If you just ended your cycle last week, you probably haven't even ovulated yet so I would have to say no to the pregnant. Although breast feeding full time will usually delay your period, it is not a fool proof form of birth control.